Carol-singing was a folk tradition appropriated by the church for its Christmas festival. Photograph: Don Hammond/Alamy

Very many of us will have a sound or a smell or a sudden temperature drop that, for each, signals the beginning proper of what, in its broadest and most literal sense, we might term the festive season.

For some, it is the first glimpse of a Christmas tree in a neighbour's window; others, the making of early gift lists; or the first Christmas card dropping on the mat; or the curious mix of cinnamon and alcohol that we find rather less appealing at other times of the year.

Even those for whom the Christian and Christianised rites of this time of year have no religious or cultural resonance have their own markers that the long nights of winter will, at last, begin to shorten – a fact humanity has celebrated with giddy enthusiasm, I don't doubt, since we first became aware of the fact.

My own first sign of the season, perhaps like yours, is nostalgic and rather sentimental and ever so slightly silly – the Christmas carol.

I love carols. I love their crashing chords when performed with bombast on church organs, and their thick layer of schmaltz when sung by Bing Crosby or Elvis, and the wobbly descant parts which, when belted out with enthusiasm by amateur choirs, never fail to make me giggle. Oh, Come!

But I also love the fact that in a season that some Christians would like to claim exclusively as their own, carols, perhaps counter-intuitively, speak profoundly of the rich and ancient connection that all of us, godly, other-godly, and godless alike, have at this time of year with traditions of festivity and the year's rebirth.

Carols originated, of course, in a form that had nothing to do with Christmas, or even with Christ. The old French carole, a ring dance with song, may derive from the Greek choros, a circling dance associated with fertility rites and celebration. Like so many other traditions, the carol was appropriated by the church for its nativity festival. Fa-la-la-la-la la-la-la-la! Or, if you prefer, Gloria in excelsis Deo!

At their purest these are songs of the people, originating in folk tunes or localised customs, stories and homespun theology. Though most of what was no doubt a rich regional variation has been lost, a few – the Sussex Carol ("On Christmas night all Christians sing"), the Coventry Carol ("Lullay, lulla, thou little tiny child") – still retain local roots; both may be of late medieval origin. Deck the Halls was a Welsh new year carol appended to Christmas when translated into English, and still, of course, has nothing overtly to do with Christianity. Here We Come A-wassailing speaks to a widespread tradition that remains a favoured festive pursuit.

Nor do these folk rhythms and resonances belong exclusively to a European tradition. I Wonder as I Wander, an unsettling carol that expresses amazement that Jesus "was born for to die for poor orn'ry people like you and like I", was overheard in Cherokee country, North Carolina, in the early 20th century and is unknown in earlier forms.

Ian Bradley, editor of the fascinating Penguin Book of Carols, to which I am indebted, argues that while the calypso carol The Virgin Mary Had a Baby Boy was collected in Trinidad in the 1940s, the structure of its chorus ("He come from the glory") suggests the music was originally brought from west Africa on the slave ships.

Similarly, while Christians will have a particular affinity with carols, they cannot claim possession, not least because they have historically been so ambivalent about them. Carol-singing in English churches was hampered by the Reformation and banned outright by the Long Parliament in the 17th century.

For much of the 18th century, the only carol sanctioned by the Church of England was While Shepherds Watched Their Flocks By Night, seen at the time as an appropriately literal rendering of St Luke's gospel, but now so heavily parodied that to many it will conjure images of shepherds, sheep and a string of freshly laundered socks stretched between Judean boulders. (That carol's author, incidentally, was Nahum Tate, whose other principal claim to fame was rewriting King Lear so that everyone lived happily ever after, deemed a great improvement on Shakespeare by Dr Johnson.)

Even those carols that appear profoundly religious may be anything but. In one of the most fascinating stories associated with carolling, there is persuasive evidence that Oh Come, All Ye Faithful, arguably today the most popular of the lot, has its origins not in a spontaneous call to worship but in something considerably more political.

It now seems likely that Adeste Fideles, the Latin hymn from which the carol was translated, was not composed by a medieval mystic as was once thought, but by John Francis Wade, a Jacobite loyalist who may have written it as a coded call to arms to those loyal (the "faithful") to the exiled Bonnie Prince Charlie on the eve of the 1745 Jacobite rebellion. In those terms, the Bethlehem to which loyalists are summoned can be read as England, while the line translated as "Come and behold him, born the king of angels" may in fact contain a pun on "regem anglorum", the king of the English. The irony of this carol's cherished position in the evangelical Protestant canon is rich indeed.

One reading of The Twelve Days of Christmas, similarly, suggests that the items given by "my true love" may in fact have been designed as a primer for young Catholics at a time when open instruction in their faith was suppressed.

If I may cite a personal favourite carol story, James Montgomery, author of Angels from the Realms of Glory, was a journalist and editor of a radical Sheffield newspaper imprisoned for his reporting of a street protest in which two died after being attacked by a militia. The name of his largely forgotten paper lives on in the title of that carol's melody, Iris.

Carols, in other words, may be to some an expression of religious devotion, but they are also drenched in the political, social and folk memory of Britain and Europe and beyond. They do not belong to theologians or hymnodists or even to those who can carry a tune, but to poor orn'ry people like you and like I. In whichever terms we prefer to understand it, carols express a very human sense of celebration that new life, very soon, is coming. Rejoice and be merry!

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